Twenty years of research evidence in animals and humans have established a biological plausibility to an association between methamphetamine exposure and PD and parkinsonism. In contrast to the many preclinical studies in this area, to date only a handful of clinical and epidemiological studies have investigated this important issue. Further studies across a range of clinical populations are needed to explore the association of methamphetamine and risk for PD and parkinsonism throughout adult life. There is some evidence that methamphetamine use may be an initiating factor Parkinson’s disease but this needs to be treated with caution and requires more evidence from large scale population studies.

Nevertheless, Parkinson’s disease is rare before age 60 and very rare before age 50. Manifestations of PD or parkinsonism in younger people, therefore, should be treated with concern and a detailed history of prior exposure to methamphetamine and/or other prescribed and illicit substances should be sought. Individual risk factors as discussed above should be identified. Premature onset of PD at any age may warrant enquiry about current or prior methamphetamine use. It is important to document the use patterns and time course of methamphetamine exposure, and to note smoking history.

Clinicians caring for methamphetamine users should be vigilant in examining for the characteristic motor symptoms of PD and for the less well-known prodromal symptoms of constipation, reduced sense of smell, and sleep disorders which may precede the onset of motor symptoms by up to twenty years (Savica et al., 2010Savica et al., 2010). Where indicated, screening for parkinsonian motor features with sensitive instruments of motor function should be conducted, designed to detect subthreshold parkinsonian features among current or previous methamphetamine users.